Tobacco-smoke filters

ABSTRACT

A tobacco-smoke filter comprising a porous tube of smokefiltering sheet material extending substantially longitudinally and preferably coaxially within an outer tubular case has longitudinal internal ribs or flutings by which the said tube is supported, spaces within the tube and between it and the case being closed at opposite ends so that smoke entering the filter at one end is constrained to pass substantially radially through the porous tube before reaching the other, outlet, end. The tube may comprise two or more layers or sections of smoke-filtering sheet material.

United States Patent Horsewell et al.

[ Oct. 15, 1974 TOBACCO-SMOKE FILTERS Inventors: Henry George Horsewell; John Anthony Luke, both of Southampton, England Assignee: British-American Tobacco Company Limited, London, England Filed: Aug. 21, 1973 Appl. No.: 390,249

Related US. Application Data Continuation of Ser. No. 165,686, July 23, 1971, abandoned.

US. Cl. 131/261 B, l31/10.7 Int. Cl A24d 01/04, A24f 07/04 Field of Search 131/105, 261 B, 10.7

References Cited UNITED STATES PATENTS Waugh 131/261 B UX Heskett et al 131/105 Lubbe 131/261 B Primary Examiner.lerome Schnall Assistant Examiner.lohn F. Pitrelli Attorney, Agent, or Firm-Kane, Dalsimer, Kane, Sullivan and Kurucz [5 7] ABSTRACT 'A tobacco-smoke filter comprising a porous tube of smoke-filtering sheet material extending substantially longitudinally and preferably coaxially within an outer tubular case has longitudinal internal ribs or flutings by which the said tube is supported, spaces within the tube and between it and the case being closed at opposite ends so that smoke entering the filter at one end is constrained to pass substantially radially through the porous tube before reaching the other, outlet, end. The tube may comprise two or more layers or sections of smoke-filtering sheet material.

3 Claims, 3 Drawing Figures TOBACCO-SMOKE FILTERS This is a continuation of application Ser. No. 165,686, filed July 23, 1971, now abandoned.

This invention concerns improvements relating to cigarette and other tobacco-smoke filters. An object of the invention is to provide a simple kind of filter by which required filtration efficiencies, including high efficiencies, can be readily obtained.

A filter in accordance with the invention comprises a porous tube of paper or like smoke-filtering sheet material extending substantially longitudinally within an outer tubular case or wrapper (hereinafter referred to as a case) having longitudinal internal ribs or flutings by which the said tube is supported, spaces within the tube and between it and the case being closed at opposite ends so that smoke entering the filter at one end is constrained to pass substantially radially through the porous tube before reaching the other, outlet, end.

For example, particularly in the case of a cigarette filter, the space between the tube and relatively impermeable material of the case may be closed at the tobacco-adjacent end by a substantially impermeable annular seal. At the other, mouth-adjacent, end, the tube may be closed by a disc-shaped plug of substantially impermeable material.

Embodiments of the invention by way of example will now be more fully described with reference to the accompanying drawing, in which:

FIG. I is a longitudinal section, taken on the lines Il-in FIG. 1, through a cigarette filter comprising a single filter tube,

FIG. 2 an end view of the filter, seen from the left in FIG. 1, and

FIG. 3 a longitudinal section, similar to FIG. 1, through a filter comprising three filter tubes.

Referring to FIGS. 1 and 2, the filter illustrated comprises a tube 1 of smoke-filter paper located co-axially within a case 2 of a substantially smoke impermeable plastics material, suitably a polyethylene or co-polymer material. The tube 1 is supported in the case 2 by longitudinal internal ribs 3 formed integrally with the latter, for instance by extrusion or molding. At the mouth end of the filter, the interior 4 of the tube 1 is closed by a plug 5 of substantially smoke-impermeable material, for example of extruded foam polyethylene, nylon or polyurethane or of a white cellulose acetate rendered impermeable by the use of a high concentration of plasticizer. At this end, the relatively narrow annular space 6 between the tube 1 and case 2 is open. At the other end, adjacent to the tobacco rod of the cigarette (not shown), the interior 4 of the tube 1 is open, whereas the annular space 6 is closed by an intumed lip 7 on the case 2. Such a lip may be produced by the application of heat. A seal at this point may be assisted by adhesive, for example, a polyvinyl-acetate adhesive.

When such a filter is in use, attached to a cigarette by an outer wrapper in conventional manner, smoke enters the interior 4 of the tube 1, whence it can pass radially through substantially the entire cylindrical wall of the tube 1 into the annular space 6 and thence to the mouth end of the filter (All as indicated by the arrows in FIG. 1). The filter material of the tube 1 can have a long effective length which, moreover, can readily be designed to obtain a required pressure drop. The external appearance of the filter remains clean and is substantially non-staining.

A filter may comprise two, three or even more coaxial tubes of smoke-filter paper either substantially in contact with each other or spaced apart radially. FIG. 3 illustrates an example of this nature in which there are three tubes la, lb and Ic in contact with each other. At the ends, the tubes la, lb, 10 are sealed together by adhesive applied at 8 and at 9 respectively. The action of the filter is as described above, except that the smoke passes through three paper walls or layers.

Specific examples of results obtained with such filters will now be briefly described:

EXAMPLE I A single-section filter, 20 mm long, of the kind illustrated in FIGS. 1 and 2 comprised a tube 1 made of smoke-filter paper having a thickness of 0.142 cm and weight 245 g/m and supported in a case 2 of impermeable plastics material, the ends of the filter being blocked in the ways described above. The filter was attached to a cigarette, the open end of the tube 1 being adjacent to the tobacco rod. On smoking the cigarette through the filter, which produced a pressure drop of 0.79 cm water gauge, under standard conditions of l puff per minute of 35 ml volume and 2 seconds duration, the overall filtration efficiency was found to be 40 percent.

EXAMPLE 2 A filter comprising two co-axial tubes of paper of the kind referred to in Example 1 was similarly attached to a cigarette. On smoking the cigarette through the filter under the same standard conditions, the filter, having a pressure drop of 2.00 cm, gave a filtration efficiency of 60 percent.

EXAMPLE 3 A filter comprising three coaxial tubes of paper (FIG. 3) of thickness 0.084 cm and weight 160 g/m was similarly attached to a cigarette. On smoking the cigarette through the filter, having a pressure drop of 2.73 cm, a filtration efficiency of 69 percent was observed.

Such filtration efficiencies compare very favorably with those obtainable from cellulose-acetate filters giving similar pressure drops. As will be understood, however, the choice of paper has an influence on filter efficiency.

Two or more filters or filter sections comprising filter tubes 1 and a common case 2 of cases may be used in series or tandam arrangements. For example two tubes 1 may be arranged, each similarly to the tube 1 in FIGS. 1 and 2, within a common internally ribbed case, the two tubes being disposed end to end with a short longitudinal gap permitting smoke from the annular space 6 of the tobacco-adjacent section to enter the interior 4 of the mouth-adjacent section. With two such sections each 10 mm long and giving a pressure drop of 5.3 cm water gauge, an overall filtration efficiency of 70 percent was observed.

The case 1 may be ribbed or fluted externally'as well as internally. Ribs may be formed by corrugating the material, for example paper or a plastics material. The case may itself be enclosed in an outer wrapper of impermeable paper or other conventional outer material used for cigarettes or mouthpieces. Plugs 5 may alternatively be made of wax.

Instead of being arranged end to end, two or more filter tubes of increasing length and diameter may be arranged to extend one inside or into another, the smoke inlet being, say, to the interior of the smallest, innermost, filter and the outlet from the annular space between the outer case and the impermeable plug closing the outermost filter at the mouth end.

If desired, the dispositions of the plug 5 and sea] at 7 may be interchanged. Particularly in this case, a conventional filter plug may be arranged in the mouth end of the filter tube, thereby producing a pressure drop which causes the smoke to pass preferentially through the porous material of the tube. Alternatively, filter plugs may be provided in both ends of a filter tube.

The paper or other filtering material of the tubular filter or filters may be impregnated with one or more additives in order to obtain selective filtration properties, such for example as one or more of sodium carbonate, zinc acetate, polyethylene imine, cellulose acetate and the like. Similarly a filling of a gas vapor phase absorbent, such as granular activated carbon, may occupy a part or the whole of the interior of a tubular filter or filters. A similar filling of a catalyst, for example manganese dioxide, may be provided. The use of such a catalyst is described in the Specification of U.S. patent application Ser. No. 132,210. The filter tube or tubes may contain one or more rupturable capsules containing a liquid serving to enhance the filtration effect or to influence the flavor of the smoke.

Papers of different porosities may be used to provide filters having different required filtration effects. Papers of different porosities may also be used in different sections of a filter or different filters of a multiple filter.

Above-described ancillary features of tubular filters may be employed in combination.

We claim:

1. A cigarette filter for tobacco smoke comprising a porous tube of thin-walled filter paper and an external supporting one piece tubular case of plastics material, within which the tube extends longitudinally, the case being formed with longitudinal internal ribs extending over substantially its whole length by which the tube is directly contacted and supported throughout its length in substantially annular spaced relation with respect to the case, spaces within the tube and between it and the case having closures at opposite ends, the closure at one end being an annular seal between the rim of the case and the rim of the tube which is constituted by an inturned lip formed from the plastics material of the case and fused to the tube, whereby smoke is prevented from passing between the case and tube at one end, and the closure at the other end being in the form of a plug mounted in the other end of the tube to prevent smoke from passing through the outer end of the tube so that smoke entering the filter at one end is constrained to pass substantially radially through the filter-paper tube before reaching the other, outlet, end.

2. A filter according to claim 1, wherein the porous tube and the case are co-axially disposed.

3. A filter according to claim 1, wherein the smoke filtering material carries one or more smoke-enhancing additives. 

1. A cigarette filter for tobacco smoke comprising a porous tube of thin-walled filter paper and an external supporting one piece tubular case of plastics material, within which the tube extends longitudinally, the case being formed with longitudinal internal ribs extending over substantially its whole length by which the tube is directly contacted and supported throughout its length in substantially annular spaced relation with respect to the case, spaces within the tube and between it and the case having closures at opposite ends, the closure at one end being an annular seal between the rim of the case and the rim of the tube which is constituted by an inturned lip formed from the plastics material of the case and fused to the tube, whereby smoke is prevented from passing between the case and tube at one end, and the closure at the other end being in the form of a plug mounted in the other end of the tube to prevent smoke from passing through the outer end of the tube so that smoke entering the filter at one end is constrained to pass substantially radially through the filter-paper tube before reaching the other, outlet, end.
 2. A filter according to claim 1, wherein the porous tube and the case are co-axially disposed.
 3. A filter according to claim 1, wherein the smoke filtering material carries one or more smoke-enhancing additives. 